Electric arc apparatus



March 16, 1943. 1.. A. MATHESON ETAL 2,314,007

ELECTRIC ARC APPARATUS Filed July 24,1941 2 Sheets-Sheet l INVENTOR.

Lorne A. Malheson BY Floyd C. l-lach Meyer Del/12:15

A 7 Tomi Y5 March 16, 1943. 'L. A, MATHESON ETAL. ,3 07

ELECTRIC ARC APPARATUS 5 Filed July 24,- 1941 2 Sheets-Sheet 2 //O Vol/.5

INVENTOR. Lorne AMa/heson Floyd C. Hack BY Mayer P. Del-1 005 A TTOLINE Y5 Patented Mar. 16, 1943 ELECTRIC ARC APPARATUS Lorne A. Matheson, Floyd C. Hack, and Meyer P. De Haas, Midland, Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Michigan Application July 24, 1941, Serial No. 403,884 Claims. (Cl. 176-41) This invention concerns an improvement in electric arc apparatus and, in particular, relates to an apparatus which provides for equal wear of electrodes.

In a co-pending application of Matheson and Hunt, Serial No. 243,734, filed December 3, 1938, now U. S. Patent No. 2,263,443, issued November 18, 1941, there is described an apparatus for the manufacture of acetylene by the cracking of liq uid hydrocarbons which utilizes series-operated alternating current arcs, In that apparatus the electrode mechanism comprises: two fixed electrodes connected to opposite poles of an alternating current source, an electrically conducting rot'or mounted between the fixed electrodes and adapted to rotate in synchronism with the alternating voltage, and two electrode arms in series with each other mounted on said rotor in such positions as to be brought into substantially simultaneous arcing relationship with the two fixed electrodes by the movement of the rotor.

In such apparatus the polarity of the fixed electrodes changes with each cycle of the alternating current. On the other hand, the polarity of each of the rotor electrode arms remains constant, i. e. the direction of current flow therethrough remains the same, since the position of the electrode arms is reversed with each reversal of the alternating current. Hence, in the apparatus referred to and in other series-operated electrode mechanisms having rotor electrode arms of constant polarity, there is usually a tendency for one of the rotor electrodes-and it is usually the anode, i. e the one into which the electric current flows-to wear away faster than the other; such wear will normally continue until the arc gap between the worn rotor electrode and the fixed electrodes is sufficiently wide to prevent an arc from striking. If,-to ofiset the effect, the fixed electrodes should be moved in close enough to contact the worn rotor electrode arm they would eventually collide with the other less worn rotor electrode arm. If, however, the rate of wear on the two rotor electrode arms is made is approximately equal, the fixed electrodes can be moved in slowly to compensate for this wear and the arc gap can be maintained at a width sufficiently small to insure that the arcs will not fail to strike.

It is, therefore, an object of this invention to provide for the more emcient operation of alternating current arcs by controlling the relative wear on the electrodes. It is a further object to provide means for reversing the direction of current flow through the rotor electrode arms.

We have now found that the relative wear of the electrode arms can be controlled by repeatedly reversing their polarity, i. e, the direction of current flow therethrough. We have also provided means for reversing the polarity either at the will of the operator or by automatic mechanisms. The invention, then, consists in the repeated' reversal of the direction of current flow through the electrode arms and the means for carrying out said reversal hereinafter fully described and particularly pointed out in the claims, the annexed drawings, and the following description setting forth in detail certain means for carrying out the invention, such disclosed means illustrating, however, butseveral of the various ways in which the principle of the invention may be used.

In the annexed drawings:

Fig. 1 is a side elevation, partly in section, of

an electric arc apparatus to which the principle of the present invention is particularly applicable.

Fig. 2 shows a plan view of the electrode elements shown in Fig. 1 and, in conjunction therewith, a wiring diagram illustrating a specific embodiment of the present invention. This embodiment consists of an apparatus in which the reversal of the current flow through the rotor electrode arms is controlled by the operator.

Fig. 3 shows a plan view of an alternative speciflc embodiment of the present invention, 1. e., one in which the mechanism for reversing the current flow through the rotor electrode arms is responsive to the width of an arc gap.

Referring now to the drawings, Fig. 1 shows a reaction chamber 6 provided with an inlet 5 for material to be subjected to the action of the arc and an outlet 6 for the reaction products. Fixed electrode mechanisms are inserted through the side walls of the reaction chamber and may be horizontal as shown or inclined. The fixed electrode mechanism consists of carbon electrodes 1, I, held in position by steel supporting rods 8, 8', to which are attached cables 9, 9' for supplying alternating current to the electrodes. The

steel supporting rods 8, 8' are insulated from the walls of the reaction chamber by porcelain members l0, l0, and may be moved longitudinally to compensate for wear of the electrodes 1, l. A rotating central electrode mechanism is inserted through the top of the reaction chamber 4. This mechanism comprises essentially the electrode proper H, a shaft I2 for rotating the electrode proper H, and a synchronous motor i3 for driving the shaft 82. The driving motor I3 is insubottoms of the waves.

lated from the shaft l2 by a shaft section l4 of insulating material. The shaft 12 enters the top of the reaction chamber through a suitable stuffing box i5 which is insulated from the chamber walls by a porcelain member I6. The electrode proper consists of a conducting disc I! and two electrode arms |8, |8 attached thereto. The electrode arms may be straight rods or may be L-shaped as illustrated in the drawings.

Fig. 2 shows diagrammatically the conducting elements shown in Fig. 1 and a wiring diagram of the external power source of alternating current for these elements. Fig. 2 also shows a control circuit for regulating the fiow of current to the motor i3. A source of high voltage alternating current provides single phase current through the cables 9, 9 to the fixed electrades 1, and three phase current to the motor |3. The current fiows through the cables 9, 9' to the fixed electrodes l and across the electrode gaps between the fixed electrodes 1, l and the rotating electrode arms l8, IS. The single phase circuit contains inductances |9, IQ for controlling the arc. The motor i3, which drives electrode arms l8, I8, is inserted in the three phase current circuit by means of a three phase step-down transformer 20. The control circuit comprises, in series, a commutator 2|, which is attached to the rotor shaft i2, but is electrically insulated therefrom; a power relay 22 which is capable of operating a switch 23 in the three phase circuit supplying the motor l3; the switch being held dosed by a spring 23a, two half wave rectifiers 24 and 25 in parallel, arranged so that one permits the current of the control circuit to fiow in one direction, and the other permits the current the fiow in the other direction; a switch 26 which controls the fiow of current to one of the rectifiers 24; and a switch 21 which controls the flow ofv current to the other rectifier 25. The switch 23 may open all three leads in the three phase circuit as shown or may open just one if it is merely desired to reduce the current to the motor I3. A transformer 28, inserted in the high voltage circuit, supplies 110 volt current to the control circuit.

Therefore, according to one embodiment of the invention, as illustrated in Fig. 2, the direction of current flow through the rotor arms can be reversed at will. The reversal is attained by causing the synchronous motor l3 to slip and then restart when the arc current has' passed through a half cycle. The slipping of the motor is controlled by a relay 22, preferably a highspeed relay, which, in turn, is actuated by the 110 volt control circuit. The control circuit consists of a series arrangement of two half-wave rectifiers 24, 25 in parallel, a commutator 2| at.- tached to the rotor shaft I2, and a relay adapted to actuate the switch 23 in the three phase motor circuit when current is fiowing in the control circuit.

The parallel rectifiers are set so that one of them transmits the alternating current in one direction-e. g., the tops of the wave-while the other transmits the reverse current, i. e., the Hence, by opening a switch 26 or 21 in either of the parallel rectifier circuits, either the tops or bottoms of the alternating current waves may be cut oiT as the case may be,

The commutator 2| on the rotor shaft is constructed so .as to be capable of transmitting only a half cycle and may be adjusted to transmit either the tops or bottoms of the alternating cycle waves, but not both.

Thus, if the rectifier switches are set for the transmission of tops and the commutator 2| is set for the transmission of bottoms, there will be no current in the control circuit. It is the same if the settings of both rectifiers and commutator are reversed. However, if one of the switches, e. g. 26, in the rectifier circuit is closed and the commutator is set to let through the same half cycle of the current as the rectifier 24, there will be a current in the control circuit. This current will actuate the relay 22 which, in turn, will open the switch 23 and shut off the current to the synchronous motor |3. As a result the motor i3 will slow down or slip and the commutator 2|, which is on the rotor shaft, will slip out of phase with the rectifier 24. When the commutator has slipped one-half cycle, it will oppose the rectifier 24, and no current will fiow in the control circuit. Hence, the relay 22 will cease to hold the switch 23 open, and the latter will be instantly closed by the spring 23a. Current will again fiow to the motor I3, and the latter will return to its normal speed, The over-all effect is that the rotor has slipped one-half cycle behind the arc current, and the direction of current fiow through the rotor electrode arms has reversed. If it is now desired to again reverse the direction of current flow through the electrode arms, the switch 26 is opened, and the switch 21 is closed. The rectifier 25 is thus placed in phase with the commutator 2|. Current again fiows in the control circuit, the relay 22 is actuated, the switch 23 opens, and the motor and the commutator 2| slip one-half cycle. When this occurs, the commutator now opposes the rectifier 25, no current fiows in the control circuit, the switch 23 closes and the motor again returns to its normal speed.

Fig. 3 shows diagrammatically the conducting elements of Fig. 1 and, in addition, a wiring diagram of an alternative control circuit for changing the direction of current fiow through the electrode arms I8, l8. The arc circuit contains, in addition to the elements of the arc circuit shown in Fig. 2, an excitation circuit 29 between one of the fixed electrodes 1' and the central rotating disc l'l, said circuit containing an inductance 30, or other impedance such as resistance, and a polarized relay 3| which actuates a switch 32 in the control circuit, the switch 32 being normally held open by a spring 32a. The control circuit contains, in addition to the switch 32, a power relay 33 which actuates a switch 34 in the three phase current supplied to the synchronous motor l3, The switch 34, which is normally held closed by a spring 34a, may open all three leads, as shown,or may open only one if it is merely desired to reduce the current to the motor.

The fixed electrode 1 to which the excitation circuit is connected is so placed that it is not diametrically opposite the other fixed electrode 1, but is displaced a short distance in the direction of rotation of the electrode arm Hi.

The excitation circuit 29, since it connects the fixed electrode 1 with the moving electrode arm I8, equalizes the potential between these two elements, placing the entire available line potential across the other electrode pair, the electrode arm i8 and the fixed electrode 1. In this manner, the entire voltage of the source will be across the fixed electrode 1 and the electrode in the excitation circuit 29.

arm l8 when these electrodes have reached their minimum distance of separation and an arc will strike between these electrodes. When this occurs, the major voltage drop will be across the inductance 30 because of the relatively low resistance of the newly formed arc, and practically all the line voltage will be imposed on the gap between the fixed electrode 'l' and the electrode arm H8. The are then strikes in this gap. During the interval between the striking of the arc in the first gap and the striking of the arc in the second gap, further rotation of the central rotor brings the electrode arm 18' to its shortest distance of separation from the fixed electrode 7. However, the striking of the arcs in the two electrode gaps will be sufiiciently close together so as to be practically simultaneous.

The embodiment of the invention shown in I Fig. 3 is illustrative of automatic control mechanisms, i. e., mechanisms which are responsive to the arc current and reverse the direction of current flow through the electrode arms whenever excessive wear on an electrode arm causes a failure of the arc to strike. The essential feature of this embodiment is the polarized relay 35, which is actuated by a unidirectional current Such a unidirectional current is caused by the failure of an arc to strike from a worn electrode. Thus, if one of the electrode arms, e. g. I8, is worn so that an arc will not strike from it, there will be no arc current in either of the electrode gaps when the worn electrode I8 is opposite the fixed electrode 1. However, when the worn electrode i8 is opposite the fixed electrode 1', there will be a current across the gap between the relatively unwom electrode arm l8 and the fixed electrode l via the excitation circuit 29. Since this latter current is conducted in alternate half-cycles, it is unidirectional. Since the polarized relay 3| is capable of being actuated by a unidirectional current in only one of the two directions, it is usually set to respond to failure of the are current to enter a worn anode, i. e. that one of the rotating arms l8 and 18' which is positive with respect to the other during fiow of the arc current, since this positive rotor electrode usually wears the most. However, if the conditions are such as to cause excessive wear on the rotor cathode, i. e. that one of the rotor electrodes i8 and 18' which is normally negative with respect to the other, the relay can be made to respond by simply reversing the relay coil or by reversing the magnet of the relay.

Thus, if the polarized relay is set so as to be responsive to a failure of an arc to strike from a worn anode, the following occurs: When the anode, e. g. electrode arm l8, becomes worn and no arc strikes between the electrode arm l8 and one of the fixed electrodes, e. g. electrode 1, there will be no current in the arc circuit or excitation circuit. When the worn electrode arm I8 is opposite the fixed electrode arm I, there will likewise be no are between these electrodes, but there will be an arc struck in the gap between the relatively unwom cathode, i. e., the electrode arm 18', and the fixed electrode 1, the current being supplied through the excitation circuit 29. The current, being conducted through the excitation circuit in alternate half-cycles, is a unidirectional current and will actuate the-polarized relay 3 I. The relay 3| then closes the switch 32 and thus energizes the control circuit which in turn actuates the power relay 33 which opens the switch 34 in the high voltage circuit supplying the motor [3. The opening of the switch 34 in the motor circuit causes the motor to slip. When the motor has slipped a half-cycle behind the arc current, the polarity of the electrode arms 1,1, i. e., direction of current flow therethrough, is reversed. A failure of an arc tostrike from the short electrode arm, which has become the cathode, will cause a unidirectional current in the excitation circuit opposite that which actuates the relay 3|. The latter will then release the switch 32, which opens, deenergizing the relay 33, and allowing the spring Mo, to close the switch 35; the motor will resume its normal speed. Meanwhile, the fixed electrodes 1 and 1' can be moved in manually or automatically a sufilcient distance to cause an arc to strike from the worn electrodes. The unwom electrode now serves as anode until it is worn enough to cause a repetition of the above sequence of events.

We have found that the repeated reversal of the direction of current flow through the electrode arms in accordance with the present invention results in an increased efilciency of operation of series-operated alternating current arcs. By operation in this manner arc failures resulting in decreased efficiency of operation, and electrode collisions resulting in mechanical abrasion or complete destruction of the electrodes are considerably reduced.

We claim: 1. In an electric arc apparatus, in combination with a source of alternating current; two fixed electrodes attached to opposite poles of the current source; an electrically conducting rotor mounted between the fixed electrodes and means for rotating the rotor in synchronism with the alternating voltage; two electrode arms in series with each other mounted on said rotor in such position as to be brought into substantially simultaneous arcing relationship with the fixed electrodes by the movement of the rotor; and means responsive to the width of an arc gap between a fixed and a rotor electrode for changing the direction of current flow through the rotor electrode arms.

2. In an electric arc apparatus, in combina tion with a source of alternating current: two fixed electrodes attached to opposite poles of the current source; an electrically conducting rotor mounted between the fixed electrodes; two electrode arms in series with each other mounted on said rotor in such position as to be brought into substantially simultaneous arcing relationship with the fixed electrodes by t e movement of the rotor; a synchronous motor for rotating the rotor; and a control circuit for the current supplying the synchronous motor, comprising, in series, two half-wave rectifiers in parallel, each conducting current in a direction opposite that of the other, a switch for each rectifier, a commutator attached to the rotor shaft, and a relay energized by current in the control circuit and connected to interrupt the current to the synchronous motor.

3. In an electric arc apparatus, in combination with a source of alternating current: an electrically conducting rotor, two electrode arms mounted oppositely on said rotor; twofixed electrodes of polarity opposite one another disposed in such position as to be brought into substantially simultaneous arcing relationship with the electrode arms by the movement of the rotor, one of said fixed electrodes being in a position displaced slightly in the direction of rotation from that diametrically opposite the other fixed electrode; a synchronous motor for rotating the rotor; an excitation circuit between the rotor and the displaced fixed electrode, said excitation circuit having in series an impedance and a. polarized relay; and a control circuit energized by the polarized relay, said control circuit comprising a relay for controlling the current supplying the synchronous motor.

4. In an electric arc apparatus, in combination with a source of alternating current: two fixed electrodes attached to opposite poles of the current source; an electrically conducting rotor mounted between the fixed electrodes; means actuated by the alternating current for driving the rotor in synchronism with the alternating voltage; two electrode arms in series with each other mounted on said rotor in such position as to be brought into substantially simultaneous arcing relationship with the fixed electrodes by the movement of the rotor; and means for repeatedly reversing the phase relationship between the alternating current and the rotor drivwith the fixed electrodes by the movement of the rotor; and means for repeatedly interrupting the current to the synchronous motor to cause the same to slip a half-cycle relative to the alternating current and thus to change the direction of arc currentfiow through the rotor electrode arms.

LORNE A. MATHESON. FLOYD C. HACH. MOYER P. DE HAAS. 

